Extracorporeal blood treatments fall into a variety of categories ranging from blood oxygenation and therapeutic hypothermia to renal replacement therapies such as hemodialysis (HD). In extracorporeal blood treatments, such as HD, blood is pumped from a patient through a blood circuit and through a treatment device, such as a dialyzer. Toxins and electrolyte exchange across a dialyzer membrane to exchange with a treatment fluid. The exchange causes the removal of waste products in the blood and excess water. A substantial volume of the patient's blood may pass through an extracorporeal blood treatment system during the course of a treatment such that any heat transfer to or from the blood can upset the patient's body temperature. Systems are also known which are used to detect patient's core temperature to permit the control of the return temperature of the blood to ensure the patient's body temperature is properly controlled.